1. Field of the Invention
The present invention relates to a next generation video communication terminal and, more particularly, to a video communication terminal using internal hierarchical memories.
2. Background of the Related Art
In an age of multimedia, information is communicated with voice, text, diagrams, and the like centering around video. As a result, the size of the communicated information becomes enormous, thereby making it difficult to store in a storage media of limited capacity and transmit through a transport channel having a small capacity.
In order to process such multimedia information effectively, compression of the information is absolutely essential. Therefore, various video compression standards have developed.
ITU-T H.261 Recommendation defines a discrete cosine transform (DCT) based compression algorithm for encoding and decoding video in real-time. H.261 discusses two types of video formats, common intermediate format (CIF) and quarter-CIF (QCIF), as shown in FIG. 1.
The formats differ only in their respective picture resolution. CIF consists of 352×288 pixels and QCIF has a quarter of the CIF resolution, 176×144 pixels. Since QCIF is a quarter of CIF's resolution, four QCIF pictures as needed to construct one CIF picture.
To overcome the limitation of H.261, H.263 is recommended. H.263 is designed for a wide range of bit rates (i.e., 10 Kb/s˜2 Mb/s).
H.263 Recommendation supports five different picture resolutions. In addition to CIF and QCIF, which are also supported by H.261, there are sub-QCIF (SQCIF), four times CIF (4CIF), and sixteen times CIF (16CIF). SQCIF has approximately one half the resolution of QCIF. And, 4CIF and 16CIF have four and sixteen times greater resolution than CIF, respectively. Support of 4CIF and 16CIF allows for encoding/decoding video in accordance with H.263, so as to compete with other higher bit-rate video coding standards, such as MPEG standards.
The motion picture expert group (MPEG) has introduced standards for coding (or compression, diversity, etc.) of audiovisual information. MPEG has set up a process to provide an efficient method of reaching adequate standards for audiovisual communications.
Specifically, the new work item known as MPEG-4 aims to provide a standard to cope with the requirements of current and future multimedia applications. The MPEG-4 standard intends to support a wide range of multimedia applications, which will surely support functionalities such as security, low delay, synchronization, interworking, and the like. Some of the functionalities have already been or are being addressed by a number of other current or emerging standards. Thus, MPEG-4 standard will use similar or improved solutions, so as to address theses functionalities.
Video communication is carried out using one of the above motion video compression standards. It is a matter of fact that a video input/output format of the common form is used between two communicating terminals for data transformation.
Specifically, a mobile communication terminal securing mobility and enabling motion video communication uses three common formats, which are shown in FIG. 1, of the five formats recommended by H.263, because a quantity of video data constructing one output screen is small in general.
FIG. 1 illustrates diagrams of standard video formats according to a related art. Each format has the illustrated structure, regardless of whether the video information is color or monochrome. Namely, each of the formats is constructed with a luminance block Y and chrominance blocks Cr and Cb. Yet, in the case of monochrome, the chrominance blocks Cr and Cb are fitted with a dummy value.
FIG. 2 illustrates a block diagram of a video output structure in a video communication terminal, according to a related art. The structure includes an external bus interface block 10a interfacing external buses to an internal bus; an internal static random access memory (SRAM) 12 connected to the internal bus, so as to store video data by a common format unit; a liquid crystal display (LCD) controller 14 reading the video data stored in the internal SRAM 12, so as to output the read video data to an LCD window, one central processing unit CPU 16, and a direct memory access (DMA) port 10b. DMA port 10b provides the LCD controller 14 access to an external memory directly. In the above construction, the external buses interfaced to the internal bus, by the external bus interface block 10a, include a synchronous dynamic random access memory (SDRAM) bus and a static memory bus.
When the video output structure outputs a substantial amount of video data to the LCD, it occupies an excessive amount of the bus bandwidth. More specifically, when video data is outputted to the LCD, the controller should read one frame of video data through the bus every 1/60 sec, thereby having a serious effect on the bus bandwidth.
Many efforts have been made to prevent the performance reduction of a system due to the excessive occupation of the bus bandwidth. One result of these efforts is the system bus structure shown in FIG. 2. The video output process in a video communication terminal is explained by referring to FIG. 2, as follows.
The external bus interface block 10a interfaces the video data, which is transmitted from another terminal, to the internal bus. Additionally, it interfaces video data, which is outputted through the internal bus, to the external bus. The video data is one of the formats shown in FIG. 1.
The inputted video data are then communicated through the internal bus and stored in the internal SRAM 12. SRAM 12 has a storage capacity of 152 kbytes. SRAM 12 is installed internally because an internal memory is more advantageous than an external memory, with regard to the bus bandwidth.
LCD controller 14 reads the video data stored in the internal SDRAM 12 every 1/60 sec, through the internal bus, and then outputs the video data to the LCD. If an external memory is required for extra communication, LCD controller 14 brings the data stored in the external memory through DMA port 10b. This reduces the load of the bus bandwidth as the video data is outputted to the LCD.
For motion video transmission, the memory size requirement is changed. For example, a QCIF video transmission needs approximately twice the memory capacity as does a SQCIF video transmission, and a CIF video transmission needs about 4 times more memory capacity than does a QCIF video transmission.
A size of the video format to be communicated can be established at call set-up by both terminals communicating the data. Yet, after a call has been set up for video communication, the size of the format to be communicated is determined through negotiation, in accordance with the receiving terminal's performance.
For instance, if a first terminal can process CIF and a second terminal can process QCIF at best, the video communication between the terminals is processed using QCIF. In this case, the first terminal should use the internal memory, which has a storage capacity sufficient for storing the CIF format, despite the fact that the communication will use the QCIF format, which uses less data. Thereby, some of the internal memory space is unused.
Preferably, the structure of FIG. 2 should enable the first and second terminals to handle the same video format, thereby optimizing system efficiency.
Also, if internal SRAM 12 in one terminal has adequate memory to support a CIF video transmission but a second terminal only supports the QCIF video transmission, both terminals communicate using the QCIF video transmission. In such a case, LCD controller 14 only reads the memory area where the QCIF data is stored. During this read operation, LCD controller 14 occupies the access to internal SRAM 12. Therefore, access to internal SRAM 12 cannot be given to other processing units, such as CPU 16 and the like, at all.
In other words, the related art structure using one internal SRAM, having a fixed storage capacity, is sub-optimally efficient, considering the current video communication carried out through various formats.
The above references are incorporated by reference herein where appropriate for appropriate teachings of additional or alternative details, features and/or technical background.